1. Field of the Invention
The present invention relates generally to an optical communication system. More particularly, the present invention relates to a semiconductor laser provided for optical communication systems.
2. Description of the Related Art
In modern optical communication systems, wavelength division multiplexing (WDM) is used, in which a low-loss wavelength band is divided into a plurality of channels, multiplexed, and then simultaneously transmitted through an optical fiber.
The most typical examples of distributed Bragg reflector lasers (DBR lasers) are a sample grating distributed Bragg reflector laser and a super structure grating distributed Bragg reflector laser.
One example of the sample grating distributed Bragg reflector laser is disclosed in U.S. patent application Ser. No. 679,120 filed Jul. 12, 1996, U.S. Pat. No. 5,748,660 issued May 5, 1998 to Delorme et al., and entitled “Sample grating distributed Bragg reflector laser, very widely matchable by phase variation and process for using this laser.” In this document is disclosed a semiconductor laser comprising an active section and two sample grating sections placed on both sides of the active section.
Further, one example of the super structure grating distributed Bragg reflector laser is disclosed in U.S. patent application Ser. No. 359,186, filed Dec. 19, 1994, U.S. Pat. No. 5,497,393 issued Mar. 5, 1996 to Kyu-Seok Lee et al., and entitled “Semiconductor laser with super structure grating distributed Bragg reflector.” In this document is disclosed a semiconductor laser having several sampling periods. According to the embodiment, each of the sampling periods is provided with grating pitches of 233.5 nm, 235 nm, 236.5 nm, 238 nm and 239.5 nm, wherein the grating pitches are arranged corresponding to wavelengths of 25 periods (5837.5 nm), 5 periods (1175 nm), 25 periods (5912.5 nm), 5 periods (1195 nm) and 25 periods (5987.5 nm), respectively. Hereinafter, an effect generated from this structure will be referred to as a chirping effect.
However, the sample grating distributed Bragg reflector laser has a problem in that since it has a wide wavelength variable section but uses an electron beam lithography process, it is expensive to manufacture while having a low yield.
Alternatively, the super structure grating distributed Bragg reflector laser has a problem in that it has a narrow wavelength variable section in spite of a simple manufacturing process based upon a typical lithography process.